An X-ray Study of Strain Generation Behavior of a Steel-scale System during High Temperature Oxidation in Air

Stress generation behavior in a steel-scale system and its relations to the structural and compositional changes of the oxide scale and the steel during high temperature oxidation were investigated by an X-ray method. A high temperature furnace capable of in situ measurement of elastic strains by X-ray diffraction up to 900°C under controlled atmosphere was newly designed. With the furnace, mild steel SS 41A(1.19% Mn, 0.2% C) was oxidized in air over a temperature range of 250-500°C, the stresses and lattice constants of the steel and oxide were measured by using the sine ψ method with Kα1 radiations of Cr and Co. The stresses in the steel measured by Cr-Kα1 X-ray during oxidation at 500°C were found to become compressive after 100h oxidation, while those of pure iron, and of the steel measured by Co-Kα1 X-ray remained tensile under the same oxidation condition. A gradual decrease of lattice constant was observed in the steel after prolonged time of oxidation at 500°C, while those of the pure iron, and of the steel measured by Co-Kα1 X-ray were nearly constant. Those differences were attributed to the compositional changes of some constituents in the steel near the steel-scale interface.